Resize (gridworld) after board/grid changes in config

[kclary]

When the Gridworld grid is altered in config, the window should auto-resize during human_play. Not sure if this is a problem outside of human_play.

[jjfiv]

This is a config-ish bug.

Here we trust the size stored on config rather than calculate it from the board:
https://github.com/jjfiv/toybox/blob/interventions/tb_gridworld/src/gridworld.rs#L182

I propose we sync it with the state impl:
https://github.com/jjfiv/toybox/blob/interventions/tb_gridworld/src/gridworld.rs#L116-L119

And delete game_size from the config. It's implicit.
https://github.com/jjfiv/toybox/blob/interventions/tb_gridworld/src/gridworld.rs#L64